The spread of cancer and embryonic morphogenesis are dependent upon changes in cellular adhesiveness. The molecular basis of cell-cell adhesion is poorly understood. This proposal presents a model system for studying cellular adhesion, the sea urchin embryo. Information gained from this system should be of general importance in improving our understanding of the nature of cell-cell interaction and possible reasons for the altered adhesiveness found in malignant cells. Molecules have been isolated in the calcium-magnesium-free sea water disaggregation supernatant of Strongylocentrotus purpuratus blastula embryos that promote cellular reaggregtion in a species-specific and embryonic stage-specific manner. By using fixed S. purpuratus blastula cells as adsorbants, a subset of molecules was isolated from the disaggregation supernatant. Rabbit antibody was made against this subset to examine its localization in sea urchin embryos via indirect immunofluorescence. Specific fluorescence was observed in a blastocoelar fibrillar matrix in S.purpuratus blastula embryos but not in embryos of other species or stages. This material may represent adhesive molecules that seep between cells and play important roles in the adhesive interactions of cells during morphogenesis. Non-specific antibodies will be removed from the polyclonal, polyspecific IgG by absorption with embryonic antigenic material other than S. purpuratus blastulae. The blastula specific antibody will be used in localization studies and Fab fragments of this antibody will be screened for ability to specifically interfere with cellular adhesion of S. purpuratus blastulae. Fibrillar blastocoelar matrices will be isolated from various species and stages of sea urchin embryos and screend for specific enhancement of sea urchin embryo cell aggregation. The final components of this study will involve screening antibodies against known extracellular molecules (and the molecules themselves) in localization and adhesion studies and sucrose and Ficoll gradient isolation of high molecular weight putative adhesion molecules in the disaggregation supernatant. This system presents a homogeneous synchronous, abundant model for identification of molecules that may function in specific cell adhesion.